Pathfinder nears its destiny

Probe touches down Friday

(CNN) -- In the grand, vast, cosmic scheme of space, the tiny Mars Pathfinder probe might seem but a speck. But if all goes according to plan, that speck will take a big leap into history Friday.

The U.S. spacecraft is set to land on the Red Planet just after 1 p.m. EDT (1700 GMT). On board is the first mobile rover ever sent from Earth to explore another planet. Named Sojourner, it will maneuver its way onto the planet's surface and begin its roving less than 11 hours after the landing.

Pathfinder's arrival on Mars will coincide with the United States' patriotic Independence Day holiday -- timing which NASA, the U.S. space agency, admits did not happen by coincidence.

The mission of the Pathfinder is one of discovery, says Donna
Shirley of the Jet Propulsion Laboratory.

"I think it's very, very appropriate that we celebrate the (holiday) with a sign of bold science and a statement that America still is an exploring society seeking to make life better for our children," said NASA administrator Dan Goldin.

First visit in nearly 21 years

The last time a spacecraft from Earth landed on Mars was on September 3, 1976, when the U.S. Viking 2 spacecraft came down on the Martian surface. But the Viking spacecraft planted itself in one spot and could not maneuver around the planet's surface.

As Pathfinder nears the Martian atmosphere, the spacecraft will be pulled ever faster toward the surface, accelerating in speed from 12,000 mph (19,300 km per hour) to 16,000 mph (25,750 km per hour).

The discovery of organic traces on a meteorite from Mars last
year renewed the debate over the possibility of life on the
red planet, according to NASA administrator Daniel Goldin.

Unlike the Viking probe, which established an orbit around Mars and gradually descended, Pathfinder will literally crash land onto the surface, cushioned by balloons that will inflate just before impact. It will then bounce to a stop like a beach ball.

But this new landing technique is not without risk, and the 200-person crew monitoring the mission at NASA's Jet Propulsion Laboratory in Pasadena, California is bracing for the possibility of failure.

"We are actually thinking about all the things that could go wrong and how we might respond to them," said Richard Cook, the mission manager.

Because of the positions of the Earth and Mars at the hour of landing, it could take a nail-biting two to four hours before scientists get the first signals from Pathfinder indicating that it survived intact.

Pathfinder won't give definite answer on Mars life

Last year's news that a Martian meteorite found in Antarctica may show that life once existed on the red planet has heightened interest in the landing. But the Pathfinder mission -- planned well before that discovery -- isn't designed to provide a definitive answer to questions about life on Mars.

However, observations made by Pathfinder could help determine whether the necessary ingredients for life exist on the planet.

"It's the first step in a long-term Mars exploration program for looking at whether or not life could have started on our neighboring planet," said Matthew Golombeck, the Pathfinder mission leader.

Mars is roughly the same age as Earth, and it has an atmosphere, gravity and signs that it once contained water.

Since NASA released its findings on the Martian meteorite, other scientists have chipped away at the original findings, taking pieces of the rock and conducting their own tests.

One such researcher, Laurie Leshin of UCLA, concluded that
worm-like forms found in the meteorite were too small to
contain a strand of DNA. She also found that the globules of
carbonate were probably formed by temperature swings far too
harsh for life.

The discovery touched off a vigorous debate between scientists supporting the theory of life ...

"We're talking about varying temperature. There is no organism on Earth that lives from zero to 100," she told CNN.

Not so fast, say researchers at Stanford University in Palo Alto, California.

"Lots of the rock formed at high temperature. Our question is, did the carbonates form at high temperatures?" countered Stanford's Simon Clemett.

Pathfinder looks to shed light on that answer and others as the space frontier moves toward the next millennium.

"I think the 21st century is going to be about the whole idea of: Is the human species a single planet species or a multi-planet species? Mars will determine that," said Louis Friedman of the Planetary Society.